Catalytic conversion process with the use of a base-exchanged silica-alumina catalyst



CATALYTIC CONVERSION PROCESS WITH THE USE OF A BASE-EXCHANGED SlLICA-ALUMINA I CATALYST Paul H. Emmett, Pittsburgh, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application September 18, 1952, Serial No. 310,352

7 Claims. (Cl. 196-52) No Drawing.

of gasoline boiling range hydrocarbons which. have found wide utility as fuels for automotive and aircraft internal combustion engines. These gasoline boiling range fuels comprise hydrocarbons boiling within the range of the lower boiling liquid hydrocarbons such as the six carbon hydrocarbons to heavier hydrocarbons boiling up to 350 F. However, these conventional catalytic cracking processes have produced relatively minor amounts of the so-called heavy naphtha fraction, namely that fraction containing hydrocarbons boiling within the range of 35 0 to 440 R, which fraction includes many of the hydrocarbons boiling within the kerosenerange. In the past this has proved economically sound since the greatest need has been for gasoline boiling range hydrocarbons as internal combustion engine fuels.

While the need for gasoline boiling range hydrocarbons as internal combustion engine fuels will undoubtedly continue, recent developments, particularly in the aircraft industry, have pointed up a possible future need for fuels comprising higher boiling hydrocarbons. For example, present military jet aircraft can employ gasoline as fuel, but more advantageously utilize kerosene, a distillate having a higher boiling point range than gasoline.

The process of my invention is directed towards a catalytic conversion process for cracking high boiling hydrocarbons to lower boiling hydrocarbons in which the distribution of valuable lower boiling hydrocarbons is modified when compared with conventional catalytic cracking processes so as to produce an increase in the yield of the heavy naphtha fraction. This increase in the yield of the heavy naphtha fraction is effected without appreciably affecting the overall yield of desired lowboiling range'product constitutents which would otherwise be obtained through the use of a conventional catalytic cracking process. This'change in distribution of product is effected by substituting for the conventional cracking catalysts employed in conventional cracking processes a composite comprising a metal Selected from the group consisting of magnesium, calcium, strontium, and barium, base-exchanged onto a silica-alumina support, that is, replacing ions from the support. The metalis base-exchanged onto the support by contacting the support with a solution containing ions-of the metal and hydrogen ions. It is essential for the purposes of my invention that the sum of the pH of the solution after the contact has been effected and the Briggs, or common, logarithm (i. e. the logarithm of the base 10) of the molar metal ion concentration of the solution at the initial time of.contact be maintained in the range of 2,744,057 I Patented May 1, 1956 4 to 8, preferably in the range of 6 to 7. After this contact treatment the base-exchanged support must be washedfree of unexchanged ions of the metal. The process of my invention is effected at conventional cracking conditions such as a cracking temperature of about 700 to 1100 F.

Any of the conventional catalytic cracking process procedures can be employed in the catalytic conversion process of my invention. Thus the process of my invention may be effected by: the fixed bed procedures such as the so-called Houdry process wherein the catalystin the form of small pellets or granules is disposed in a stationary bed; the moving bed procedures such as either the so-called Thermofor catalytic cracking process or the Houdriflow process wherein the catalyst is caused to move downwardly through the reactor in a continuousbed; and the so-called fluid procedures wherein the catalyst in the form of fine particles is usually disposed in a reaction zone to which catalyst is continuously added and from which catalyst is continuously removed. Each of the afore-mentioned procedures involves the regeneration of the catalyst by burning otf coke, which is deposited upon the catalyst during the course of the process, at a temperature of the order of 1000 to 1200 F. This regeneration is accomplished on the catalyst in situ in fixed bed procedures, and ma separate regenerator in the moving bed and fluid procedures. Such regeneration of the catalyst is to be included within the process of my invention. 7

While any of the alkaline earth metals listed above can be used in the catalysts employed in my'process, I prefer barium. Moreover, a wide variety of silica-alumina supports can be employed to make the catalysts used in my process. Thus synthetic silica-aluminasupports, preferably containing from 80 to 90 percent by weight of silica with the remainder consisting of alumina are especially useful for the catalysts employed in my process. In addition, relatively minor amounts of other metal oxides such as zirconium oxide, titanium oxide, boron omde and tungsten oxide can advantageously be present. In the case of such supports, the finished catalyst should contain from 0.25 to 2.0 milliequivalents of base-exchanged metal per gram of support, and preferably from 0.80 to 1.20 milliequivalents of base-exchanged metal per gram of support.

Not only can synthetic silica-alumina supports be employed in the catalysts used in the process of my invention, but moreover argillaceous silica-alumina supports are applicable. While a wide variety of natural clays can be employed, activated montmorillonites and activated halloysite are to be preferred. In the case ofcatalysts prepared from silica-alumina clays, the amount of base-exchanged metal on the support should usually be less than that present in catalysts prepared from synthetic silica-alumina supports. It is preferable to have from'0.l to 0.5 milliequivalent of base-exchanged metal per gram of support when the support is a natural clay.

Where relatively large amounts of metal are to be base-exchanged upon the support, it is often desirable to accomplish this by first preparing a catalyst in an identical manner to that given above, namely by base-exchanging the metal onto the support by contacting the support with a solution containing ions of themetal and hydrogen ions in which the sum of the pH of the solution after the conf tact has been effected and the Briggs logarithm of the molar metal ion concentration of'the solution at the initial time of contact is maintained in the range of 4 to 8, preferably in the range of 6 to 7, and then washing the base-exchanged support free of unexchanged ions of the metal. The base-exchanged catalyst should then be cal-v cined at a temperature of the order of 750 to l300 F.,

and contacted with a further solution containing ions of the metal and hydrogen ions in the same ratio as stated above and washed free of unexchanged ions of the metal as before. In this manner greater amounts of base-exchanged metal can be incorporated onto the support than is possible by single base-exchange treatments.

The synthetic silica-alumina supports to be employed in preparing the catalysts used in the process of my invention can be obtained by a number of methods. Thus, for example, these supports may be manufactured by coprecipitating the silica and the alumina by mixing a soluble silica composition and a solution of a soluble aluminum salt under conditions of pH adapted to cause the formation of the precipitate. In this connection, it should be noted that since there isno clear line of distinction between compositions referred to as hydrogels and those referred to as gelatinous precipitates and since both these materials yield closely similar final products, both are referred to generically as gels containing water of formation or, shortly, as undried gels. In this coprecipitation method of preparation, any alkali metal present in the gel as initially formed can be removed from the wet gel which is then dried and calcined. Alternatively, the gel containing an alkali metal can be dried and the alkali metal can be removed later by base exchange, for example, with a suitable ammonium salt. The resultant product is then again dried, and is calcined to fix its physical and chemical properties.

Another method of preparing synthetic silica-alumina supports comprises first preparing a silica hydrogel by treating an alkali metal silicate with an acidic material such as hydrochloric acid, washing the resultant gel free of alkali metal, adding a solution of a soluble aluminum salt such as aluminum nitrate to the washed silica hydrogel, and then adjusting the pH of the resultant mixture to precipitate an alumina gel by the addition of an alka line material, preferably ammonium hydroxide. The excess alkalinity is removed and the mixed gel is dried and calcined.

In addition to the foregoing, synthetic silica-alumina supports can also be prepared by first making a silica gel as described above, drying, calcining, and then forming the alumina in situ by treating the silica gel with a suitable aluminum salt, and calcining. If the aluminum salt is decomposable by heat, then the decomposition of the salt and the fixing of the properties of the composite can be accomplished in a single calcination.

In order to illustrate theprocess of my invention, a synthetic silica-alumina support comprising a commercial cracking catalyst having the follow-ing analysis:

Weight per cent was oven-dried for 16 hours at 230 F. 696.7 grams of this support were soaked in 11,900 cubic centimeters of an aqueous solution containing 30.4 weight per cent of barium acetate and 0.827 weight per cent of barium chloride, a total concentration of barium ion of 1.45 mols per liter, for 3 days. This solution had a density of 1.265 gm./cc. Mechanical agitation was used during the soaking treatment to assure satisfactory contact between the support and the solution. The pH of the fresh solution was about 8.4, while the pH of the used solution was about 6.1. An identical solution that was left standing during the treating operation had a pH of 8.2. By titrating the treating solution before and after use, it was determined that about 1.05 milliequivalents of barium per gram of support had been base-exchanged onto the support. After the soaking treatment the base-exchanged support was Washed with distilled water on a filter until free of chloride ions. The washed composite was then oven-dried, and calcined overnight at a maximum temperature of about 1000 F. In the aforementioned example the pH of the solution after the contact had been effected was 6.1. The initial concentration of the barium was 1.45 molar. The Briggs logarithm for 1.45 is 0.1614. Accordingly, the sum of the pH of the solution after the contact has been effected and the Briggs logarithm of the metal ion concentration at the initial time of contact is 6.26.

The cracking activity of the base-exchanged composite was compared with the cracking activity of the silicaalumina support and also of a steam-aged silica-alumina support whose cracking activity had been reduced by aging in the presence of steam at high temperatures. The comparison was effected by catalytically cracking a Mid- Continent light gas oil having a gravity of about 35 A. P. I. at a temperature of 920 F. and recording the total conversion through the 440 F. end point fraction, the weight per cent of the C6350 F. fraction (the gasoline fraction), and the weight per cent of the 350'- 440 F. fraction (the heavy naphtha fraction). The

results obtained with each catalyst were as follows:

Milliequivalents of barium per gram of 1. 05 none steam aged.

silica-alumina support.

Conversion 68.1 52.1 47.8.

(15'350 F. traction (wt. percent) 22.41. 17.86 24.24.

350440 F. traction (wt. percent) 5. 3 9.06 5.47.

wt. percent 350-440 F. IracttonXlOO/ 7.8 17.4

11.4. conversion.

1 Conversion was measured as the percentage of the charge stock which was cracked into material bflllll'lg be ow 440 F.

It is seen from the foregoing that the sum of the Cs350 F. and 350440 F. fractions from each run is approximately the same with each catalyst. However, the yield of the 350-440 F. fraction is strikingly increased in the case of the barium base-exchanged catalyst. Thus the ratio of the weight per cent of the 350"- 440" F. fraction to the weight per cent conversion is more than twice as great for the barium base-exchanged catalyst than it is for the untreated support and is also about 1% times greater than that of the steam aged support. It is thus seen that base-exchanging barium onto the support provides a means of varying the distribution of product from a catalytic cracking conversion without appreciably affecting the yield of desired boiling range product constituents. In this manner a larger yield of the heavy naphtha fraction can be obtained and the economics of the refinery can be adjusted to meet varying market demands. Thus when gasoline fuels are desired, conventional cracking catalysts can be utilized in the catalytic cracking units. However, when the market demand shifts so that the market requirements for heavy naphtha are at a premium, the base-exchanged catalysts employed in my process can be substituted for conventional cracking catalysts and the cracking process of my invention utilized.

The process of my invention permits relatively high boiling hydrocarbon feeds to be catalytically cracked to yield increased amounts of the heavy naphtha fraction without appreciably affecting the over-all yield of desired low-boiling liquid product constituents. My process therefore permits a petroleum refiner to convert his catalytic cracking equipment to the production of increased amounts of heavy naphtha hydrocarbons by simply substituting a different catalyst for conventional cracking catalysts.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spirit or scope thereof and therc fore only such limitations should be imposed as are indicated in the appendedclaims.

The method of preparingthe catalyst employed in the catalytic conversion process of this invention isdescribed and claimed in applicant's copcndingapplication Serial No. 310,351, entitled Composite Materials and Processes for Making the Same, which was filed on September 18, 1952.

I claim:

1. A catalytic conversion process comprising cracking high boiling point hydrocarbons at a temperature of about 700 to 1100 F. in the,presence of a cracking catalyst to yield lower boiling point hydrocarbons, said cracking catalyst containing 80 to 90 per cent silica and catalyst having been prepared by base-exchanging a metal selected from the group consisting of barium, magnesium, calcium and strontium onto'a silica-alumina support selected from the group consisting of synthetic silica-alumina composites, activated montmorillonites, and activated halloysites by contacting the support with a solution containing ions of the metal and of hydrogen, the sum of the pH of the solution after the basfe exchange and the Briggs logarithm of the molar metal ion concentration of the solution at the initial time of contact in the baseexchange being maintained in the range of 4 to 8, washing the base-exchange support free of unexchanged ions of the metal, and drying and calcining the base-exchanged support, whereby 0.1 to 2.0 milliequivalents of metal are base-exchanged onto the silica-alumina support per gram of the support.

2. A process as set forth in claim 1 in which the silicaalumina support is base-exchanged with barium.

3. A process as set forth in claim 1 in which the silicaalumina support is a synthetic composite of silica and alumina and the amount of metal base-exchanged onto the support is in the range of 0.25 to 2.0 milliequivalents of the metal per gram of the support. I

4. A process as set forth in claim 3 in which the sum of the pH of the solution after the contact and the Briggs logarithm of the molar metal ion concentration of the solution at the initial time of contact is in the range of 6 to 7.

5. A process as set forth in claim 1 in which the silicaalumina support is selected from the group consisting of activated montmorillonites, and the amount of metal ion base-exchanged onto the support is in the range of 0.1 to 0.5 milliequivalents per gram.

6. A catalytic conversion process comprising cracking high boiling point hydrocarbons at a temperature of about 700 to 1100 F. in the presence of a cracking catalyst to yield lower boiling point hydrocarbons,- said catalyst having been prepared by base-exchanging a metal selected from the group consisting of barium, magnesium, calcium and strontium onto a silica-alumina support consisting essentially of a synthetic calcined silica-alumina 10 to 20 per cent alumina by contacting 'said silicaalumina cracking catalyst with a solution containing ions of the metal and of hydrogen, the sum of the pH of the solution after the base-exchange and the Briggs logarithm of the molar metal ion concentration of the solution at the initial time of contact in the base-exchange being maintained in the range of 4 to 8, washing the base-exchanged support free of unexchanged ions of the metal, and drying and calcining the washed base-exchanged support whereby about 0.25 to 2.0 milliequivalents of metal are base-exchanged onto the silica-alumina support per gram of the support.

7. A catalytic conversion process in which a high-boiling hydrocarbon is catalytically cracked in the presence i gen ions, the sum of the pH of the solution after the contact has been effected and the Briggs logarithm of the molar metal ion concentration of the solution at the initial time of contact being maitnained in the range of 4 to 8, washing the base-exchanged support free of unexchanged ions of the metal, then calcining the base-exchanged support at a temperature of the order of 750 to 1300 F. contacting the support with a further solution containing ions of the metal and hydrogen ions, the sum of the pH of the solution after the contact has been eflFected and the Briggs logarithm of the molar metal ion concentration of the solution at the initial time of contact being mainained in the range of 4 to 8, again washing the base-exchanged support free of unexchanged ions of the metal, and drying and calcining the washed baseexchanged support whereby 0.1 to 2.0 milliequivalents of metal are base-exchanged onto the support per gram of support.

References Cited in the file of this patent UNITED STATES PATENTS Spicer et a1 Nov. 18, 1947 Corner et al. Nov. 7, 1950 

1. A CATALYTIC CONVERSION PROCESS COMPRISING CRACKING HIGH BOILING POINT HYDROCARBONS AT A TEMPERATURE OF ABOUT 700* TO 1100* F. IN THE PRESENCE OF A CRACKING CATALYST TO YIELD LOWER BOILING POINT HYDROCARBONS, SAID CATALYST HAVING BEEN PREPARED BY BASE-EXCHANGING A METAL SELECTED FROM THE GROUP CONSISTING OF BARIUM MAGNESIUM, CALCIUM AND STRONTIUM ONTO A SILCA-ALUMINA SUPPORT SELECTED FROM THE GROUP CONSISTING OF SYNTHETIC SILICA-ALUMINA COMPOSITES, ACTIVATED MONTMORILLONITES, AND ACTIVATED HALLOYSITES BY CONTACTING THE SUPPORT WITH S SOLUTION CONTAINING IONS OF THE METAL AND OF HYDROGEN, THE SUM OF THE PH OF THE SOLUTION AFTER THE BASE-EXCHANGE AND THE BRIGGS LOGARITHM OF THE MOLAR METAL ION CONCENTRATION OF THE SOLUTION AT THE INITAIL TIME OF CONTACT IN THE BASEEXCHANGE BEING MAINTAINED IN THE RANGE OF 4 TO 8, WASHING THE BASE-EXCHANGE SUPPORT FREE FO UNEXCHANGED IONS OF THE METAL, AND DRYING AND CALCINING THE BASE-EXCHANGED SUPPORT, WHEREBY 0.1 TO 2.0 MILLIEQUIVALENTS OF METAL ARE BASE-EXCHANGE ONTO THE SILICA-ALUMINA SUPPORT PER GRAM OF THE SUPPORT. 